Electbical apparatus



BEST AVAILABLE com March 22, 1927. 1,621,901

W. H. PRIESS ELECTRICAL APPARATUS Original Filed Dec. 5, 1921 3 Sheets-Sheet 1 45 INVENTOR li zlliamlifliass MORNEY BEST AVAILABLE COFW 2 1 March 2, 927 w H. PRIESS ELECTRICAL APPARATUS 5, 1921 3 Sheets-Sheet 2 Original Filed Dec.

r l l INVENTOR mlliamll. Hie-9s ATTORNEY BEST AVAILABLE com March 22 1927. 1,621,?

W. H. PRIESS ELECTRICAL APPARATUS Original Filed Dec. 5, 1921 3 Sheets-Sheet 5 Patented Mar. 22, 1927.

UNITED STATES PATENT OFFICE.

WILLIAM H. PRIESS, OF MONTCLAIR. NEW JERSEY, ASSIGNOR TO WIRELESS SPE- CIALTY APPARATUS COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF NEW YORK.

ELECTRICAL APPARATUS.

Original application filed December 5, 1921, Serial No. 519,868.

Patent No. 1,499,403, dated July 1, 1924.

Divided and this ap lication filed December 5, 1923. Serial No. 678,557.

This invention relates to electrical apparatus and more specifically to electrical condensers. This application is a continuation in part of my copending application Serial No. 465,137, tiled April 33, 1921, Patent No. 1,558,043 patented 20 October, 1925, and a division of Serial Number 519,868, tiled Dec. 5, 1921, Patent Number 1399,4031 patented July 1, 1924.

Condensers and spark gaps embodying the present invention are for use generally, but in particular the spccitic embodiment in condensers herein illustrated is adapted for use to interconnect a low loss high-powered radio frequency reservoir circuit and an antenna circuit tuned to the same period. The condenser transfers the energy from the reservoir to the antenna. The condenser of this invention is characterized by being adapted for high voltages and relatively small capacity. As an example of a practical- -and commercial embodiment of such condenser, it may have a capacity of .00002 mid. and be capable of withstanding 50,000 volts etl'ective' (T0000 volts maximum), at two amperes and 600 meters maximum.

The type of condenser embodying the present invention is known as a mica condenser inasmuch as it usually comprises a stack composed of alternate sheets of ttoil'and dielec trie, the foil consisting preferably of a soft material such as lead or tin, and the dielectric consisting preferably of mica, which is one of the best dielectrics known for this purpose.

The stacks each are made up of sections connected in series vith separators between the sections, and. are clamped and secured within a suitable casing, the casing preier- 'ably in service constituting one of the terminals of the condenser, or an electrical connection between stacks.

An object of the invention is to provide a spark-gap that will ensure proper protection irrespective of careless handling of the condenser.

Another object of the invention to provide a novel form of spark-gap tor preventing excessively high ditlerences of potential between parts of the condenser and the subsequent destruction thereof.

In the accompanying drawings, I have illustrated one embodiment of the invention.

in which Figure 1 is an elevation thereof with part of the casing broken awa '5 Fig. 2 is a plan view thereof, with part of the casing broken away; and

Fig. 3 is a sectional elevation on the line 33 of Fig. 2, looking in the direction of the arrows.

Referring to the drawings, I have illustrated a casing 10 containing the condenser elements or stacks S, which casing is preferably of metal and constitutes a midpoint series connection between the stacks, or, it so desired, a terminal of the condenser. In this embodiment, the casing is divided by a metal conductive partition 11 into two chambers 12 and 13, each adapted to receive a pair of stacks S, or a two-partstack. The casing has an opening at one end, i. e., the bottom, covered by removable closure 14 common to the two chambers 12 and 13 and secured to the casing against a gasket '15 by means of screws 16. At the opposite, i. e., top endof thecondenser casing are. openings 17 throughwhich the high potential terminals and their insulators of the condenser extend, closing'thc'openings as hereinafter described, one of the openings 17 being provided'for each chamber, the bottom closure 1r, however, being common to both chambers 12 and 13, whereby the latter may be filled with a suitable insulating material V such as molten-parafiin or oil.

The stacks S consist preferably of alternate sheets of foil and dielectric, preferably mica, and are made up of sections connected in series with separators 18 between the sections in the manner illustrated in Fig. 3. The stacks of each pair are arranged horizont-ally and end to end Within the casing;

that is, the sheets composing them are arranged vertically with reference to closure 14. The inner adjacent ends of the stacks or stack parts engage a suitable metal pressure member 10 having relative high therr'no-con ductivity, the stacks being arranged in the same straight line and being compressed against the member 19 by means of a pair of metal pressure plates 20 engaging the outer ends of the stacks and compressed against the same by means of metal screws 21 thrcad cd through the casing and engaging the members the, plates 20 and screws 21: ha ring a high thermal conductivity to the car-'- ing 10. Thus the outer ends of the stacks have a high thermalsconductivitry to the metal casing which is a good radiating means. The outermost section 0'1 each stack is electrically connected to the adjacent pressure plate 20 by means of a copper strip lead 22 which is secured to the free terminal of the outermost section and bent back between the stack S or S and. the pressure member 20. The inner ends of the stacks are'in like manner electrically connected to pressure member 19 by means oi flexible copper strip leads23, which are bent backand interposed between member 19 and the inner ends of the stacks, wherebr tliv stacks are electrically connected at their outer ends to the casingas a. common conductor, and at their inner ends to member 19. Each central pressure member 19 is provided with a threaded tmening25l, in which is threaded a heavy metal rod or tern iinal which projects through the opening 17 to each chamber 12 and 13.

Inasmuch as each high potential terminal 25 must be thoroughly insulated from the casing 10, which is at an intermediate po tential, I utilize an insulating device 26 for each. In the present embodiment, this insulatingdevice comprises a disk or plate 27 of insulating material which is of an area ,greater than the area of the opening 1'! in fthe.;cas ing and extending over the bound- ;aries of said opening. This disk is prefere ably of somematerial having high'insulat- .ingqualitiescand low loss such as mica, and ,Sliould be so designed as to withstand-the difi'erence in potential between the casing'lO and terminals 25. It is preferred that the plate 27 consist of mica, which is one of the best materials for this purpese,the plate being clamped at its edge to the casinglt) by means of a. metal ring28, and screws 29 passing through the riugBS into the casing 10, a suitable gasket 2!) being interposed be- ;tween the mica sheet and the casing 10 to secure a tight joint. The, members 25 extend through the disks 27. Mounted around each terminal 25 below the plate 2? is an insulat ingbushin 31 of reduced diameter compared to plate 2?. This bushing is provided with cornn atious or grooves 33 arranged circunifercntially therearmind to increase the creepcgedistance between the. terminal 25 ,and casing 10 and consists preferably of a i n'iin ated structure; for instance, a. plurality of inica pieces or-disks of diameter reduced compared witlrthe disk 27 and compres ed tQEIthQlflifl the manner hereinafter described.

Mounted upon the opposite side of the large mica plate 27 is an insulating bushing 32 of reduced diameter compared with disk 1,6 BESTAVAILABLE COP\ 27 and surrounding and insulating the upper portions of the terminal 25. Like the l)l.l 2l: ing '31, theZ-lmshing :32 is :also otlaminuted insulating material preferably built. up oi.

superimposed pieces or disks of mica and ot' decreasu gdiameter upwardly as illustrated, fen-min an upwardly taperinghushing.

The insulating device 26 is preferably constructed or assembled on terminal 25 by assembling thereon the mica disks, plates or wrashers in their proper order. in the embodiment. herein illustrated, a nut at is threaded on the lower end of member The mica washers or pieces constituting the bushing 31 are then positioned or assembled .on member upon nut 34. then di k '27 is positioned and then the pieces consiituting the bushing 32 are-positioned on member 25. A round nut (Fig. 3) is threaded upon the upper end of member fZ-o-to hold theinica sheets and pieces in position against-dislocation. The assembly is then treate'd;in a bath of hot molten insulating mater-ial,;which will act more or less as an adhesive, for abQut. fifteen minutes until bubbles cease, either with or without the application (if-vacuum. Suitable materialsfor this purpose are beeswax, paraffin, insulation varnish-or sulfur or insulatingmixtures containing anyofthese materials. The assembly while hot-and impregnated with molten insulating-material 1S compressed or clamped tight-1y by nut 35 and allowed to cool, thus elampingt-he mica sheets-together in a solid mass held-together by nut 35 (which may be pinned tomember 25) and by the fusible insulation which has now solidified. 'The-bushine 32 is then-cut, turned or ground to proper shape andpolished, providing a -smoot-h=t-apered surface. The bushings 31 and 32 are thus retained and supported on plate 27 and held under compression entirely by means of member and nuts 34 and 'lhe-grom es 33 are formed by assembling intermediate mica washers of reduced diameter.

{Mounted on each terminal 25 above each nut 35, in close electrical contact therewith and with each member 25, is a concavo-conre metal. member 36, having its concave side facing the bushing 32 and having its rounded edge 37 concentric with and spaced=from the clamping ring 28. Such-J-nounting of me-m her 36 is by screwing member 36 down upon member 25 to any desired position of install ers or manufacturing adjust-n'ient determined by the thickness of nut 35 of Fig. 3. The inclination of the outer surface of-tbe bushing 32 and the curvature and spacing ot' the member 36 (the latter determined as aforesaid by nut are so arranged with reference to each other and so proportioned that any difi'erence of potential betweenthe opposite ends of the member 25 produces electrical stresses not through the insulator 32 but mainly through the air from member 36 lit) 1,621,901 BEST AVAILABLE COP) to the casing 10, maintaining the electrical field parallel with the bushing 32 instead of cutting the same. In other words, member 36 with casing provides a static shield preventing losses in the insulator 32 and the destruction thereof. The members 36 also perform additional functions in that they providelarge-surfaced terminals for radiating heat generated in the stacks and conducted through the terminals to members 36. The members 36 also serve as protectors or dust-guards for the insulating devices 26, preventing deterioration thereof; that is, each is located above the insulating disk 27 and the bushing 32. Each member 36 also constitutes an electrode of a spark-gap device described hereinafter. Each corona member 36 is secured in place by means of a nut 38 threaded upon the upper port-ion of the member 25, and above this are located washers 38 and nuts 39 whereby any suitable lead may be attached to the high potential terminal in the usual manner.

The stacks SS in each chamber may be adjusted as a unit by means of the two pressure screws 21 (Fig. 3), in opposite directionsto properly locate each terminal 25 with .the terminals 25 projecting through and in-. sulated from the casing.

. adjustable conical metal member 42, which.

reference to each other and with reference to its opening 17 whereby the insulating device 26 may be properly clamped in position.

It will be seen that stacks SS of each chamber are connected in parallel with one point connection between the two sets of stacks in the two chambers. Casing 10 connects the two sets of stacks in series with In order to protect the condenser against excessively high voltages, beyond a value for which the condenser is designed, I have provided a spark-gap device (Fig. 1) which co-operates with each of the shields 36 to form therewith spark-gaps. This spark-gap device comprises a metal rod or stud 40 threaded into the top of the condenser casing 10, in conductive relation thereto (i. e., connected to the midpoint of the condenser between the two sets of stacks) and between and in spaced relation to shields 36 of the two terminals 25 from the sets of stacks. The upper end 41* of the metal rod 40 is threaded. Meshing with the threaded end 41." is an may be adjusted vertically to vary the dis tances betweenits inclined surface 43 and the adjacent shields 36, providing with shields 36 spark-gaps for protecting each set of stacks SS, the length of the gaps depending on conditions specified below.

The conical member 42 may be locked by a set screw 41 after its correct location (specified below) is determined for any given condenser.

The distance between members 42 and 36 to form a spark-gap depends on the radius of curvature of adjacent portions of the two parts, the shorter the radius of curvature of such adjacent portions the greater the distance or spacing between them, must be to withstand a given difference of potential. In the present design, the distance between the member 42 and each edge 37 of each bell 36 is such as to provide the required spacing to protect the condenser for the given radii of curvature of such adjacent parts, the greater the radius of curvature of such adj acent portions the less the corona effect between the parts at a difference of potential will be and the less thedistance may be to protect each set of stacks from voltages exceeding the designed value.

The object of the spark-gap device of the present invention is to protect the condenser by preventing the user from exceeding the rated potential. Axial adjustment of comthe shields 36. The threads on stud' 40 have a very small ra'dius of curvature so that when member 42 is removed, the condenser will spark even at a potential lower than the rated voltage or lower than the voltage each set of stacks is designed to stand even though the length of each gap is thereby increased. I t stud 40 also is removed, there will be formed a single spa'rk-gapbetween'the two shields 36 protecting both 'sets' ofstacl'is against voltages exceeding those'ior which the' condenser is" designed; In like manner, when the two shields 36 constitute the spaced members of the spark-gap, the condenser will spark ovenat a potential lower than the total rated voltage, the 'radiiof curvature of the curved edges 37 being so designedto-produce this result for a given spacing between shields 36. v

I find, for example, in a commercial 'embodiment of the invention with stud 40 and member 42 in place,asillustrated, and with member 42'positioned to form a gap of 7 inch with each shield 36, the 'condenser will flash over at approximately 25,000 volts effective from either shield 36 to the member 42. lVith member 42 removed, the distance between each shield 36 and stud 40 is increased to about inch, but owing to the small radius of curvature ot stud 40 or its threads compared to that of member 42, the condenser will flash over around 24,000 or 25,000 from either shield 36 to the stud 40, still maintaining the protection below the designed value. If stud 40 is removed, the distance between the two shields is about two iaielics,-luit.iai; this case the-gap must handle the entire voltage impressed [across terminals 25 and with a given radius of curvature of t,he--e lges. 3 7, the condenser will spark 5 over at about 46,000 volts effective.

llihen stud .40 is removed, the gap formed .by the twoshields 3G=will not protect the condenser in every case because of the con- .ditionsv existing in the circuit in which the condenser isused. 111 most cases, however, .when member 42 and the stud ldhave been removed, probably through carelessness, the gap between the shields will be sufficient to ;protect the condenser. lhespark -gap de- ..15 vice above described ,and. herein illustrated as -:-fool proof. '.l. he adjustability of men) berJtQ is-a convenience in securing the correct .spacing between n'iember 42 and each shield .36. while. if member 42 is removed,

-:-,- t,l'iere is still maintained .a non-adjustable gap between stud. .40 and eachshield 36 such as to -.si,1fiiciently protect the condenser. In- .asmuch as :the-me-mbers 4L042 are. in elec- :;trical.eor 1;necti on totlieca-sing 10 (a mid .:Z5 :peintseuiesconnection between the. two sets of-=st acks) eaehgap formed between them end .oneofathe shields 36 controls only ap- ;prox imately;onerhalf of. the total impressed moltage. -But when the two shields .36.:torm the gap, .this ,gap :protects the condenser .againstmoltages exceeding the .total designed voltage, although the length oigap between the two shields is greater than twice the dista nce between each gapland conical member 65.4 2. inasmuch-as the potential necessary to --bre a;k;down-a gap .does not vary asastraight line-function of the-length of.the gap, the .lon-ger gap will break dow n, .at a potential lower: than-.twice :the potential necessary to -;b reale idownone oi the shorter gaps.

'llhe insulators26, for the-purpose of:in- .sulating --the high -potential terminals 25 1-;trom-.,the casingprovide a long. creepage path with shortheight. ,Additional creep- =age ;i s-obta:ined by,providin g circumferen- .--tial groovesin either orboth fthe mica. bnshingsrupon either or botlnsides of the mica disks 2?. I have shown such grooves .33iinit-he micahushing31. In the present .construction. eaeh insulator 126 comprises a .single-mica-diskf-2T clampedto the casing 10, andbnilt-up disks of mica. ofreduced di- .ameter forming bushings .upon and sup- -:por.ted by the :diskQT. the bushingsbeing --cla-n iped :to the disk 2?:at ,opposite sides -thereot-by means of= theanember- 25 ,and 'co- -.operatin 1 nuts threaded thereon.

-B v: the illustrated example of the, invention, instead of using one stack, 1 have used -four stacks. each-stack havingn minimum :length. consistent-withthe ereepage requirement-between the opposite ends of the stack one to.voltagewdilierences. Eaehstack has nnaxinrum thermalconductivity to the casing and-to the-high potential terminals. Each 'ellicient operation and low loss.

BEST AVAILABLE COP\ high potential terminal is PLOVltlQtl on the exterior of the condenser with ,a corona spariogap shield 36 constituting ,a heatradiating member, the casing 10 constituting the other heat-radiatin member. ,It will thus be seen that each stack, of minimum length, e'. igagcs at opposite ,ends conductors havinga high thermal conductivity mid large heat-radiating powers. The construction and method of building the stack is such thatside slip of the fillJCiS lll the stack is prevented. 'i'he presure applied to the opposite ends of each stack shouldbe of the order'o'f thousands of pounds per squnre inch, and of .an order which is slightly below a value that will cause sorczu ii .g of the foil sheets. The structure above-described issuch that the stacks are maintained at a minimum tem- -perature for a given load, which results in .In this disclosure, placing tour shortstacks,which are electrically iinseries parallel with one another and each consisting of series sections. thermally parallel-bet\\;een' highconducting terminals, the thermalpath is improved in a ratio. of approximately sixteen to one over a singlesta'ck having the same electrical characteristics. {in this arrangement, I have improved-the condenser (ionstruction -so that' it willcz rryfour times the energy of the equivalent single stack with the same heating. in .tl1e, p 1eent, invention,

also, for the,sz 1 me -capacity," I have been able to reduce the amount ofmica required' n a condenser, thus. materially reducing the-cost.

,F or instance, in a condenser'having ,asingle stack of the samejlength as the total'length of.the four stacks of the present condenser and having. the capacity ofthe-condenserof the present invention, there wouldbe re-.1 quired. n' iic a.sheets of four times the area over those required "for the condenser of this invention. Furthermore, a much more expensive clamping means would ,be required to obtain the same pressure per ,unit. area.. Such clamping means moreover would" be .inferior an'd'ineflicient asw'e'll as bulky. In

the present; disclosure, by the methods. of manutacturm g the stack as above described,

and by reason of. the minimum length ofthe stack, side sliphas been reduced to a minimum, and the clampingfeature simplified while maintaining the high pressure/ It. will be seen, therefore, that the disclosed preferred embodiment of the invention provides .a veryvefficient high tension condenser which is not only protected by the spark;gap meens claimed hereinafter, but which is .very compact, andin which the stacks are maintained under the highest practicable compression to maintain. thesheets of foil and dielectric n intimate contact to ,prevent losses in the stack and to inerease its-thermal conductivity. The casing forms a heat-eonduct-iug and radiating. device in contact-with. 139

the outer ends of the stacks. The inner ends of the stack-'5, in like manner, have high thermal conductivity to the outside through blocks 19 and terminals 25, where the heat is radiated by the heat-radiating members 36 upon the terminals.

It is to be understood that the invention is not limited to the embodiments and fertures specifically shown and described herein, but that such en'ibodiments and features are subject to changes and modifications without any departure fronithe spirit of the invention.

I claim:

1- An electrical condenser comprising a plurality of sheet-stacks; a common metal casing therefor and connected therewith; a corresponding plurality of stack terminals extending outside the casing; and a metal member electrically connected with and mounted on the outside of the casing and spaced from said terminals to constitute a common spark-gap electrode establishing protective spark-gaps with said terminals.

2. In an electrical condenser, a metalcasing, condenser elements mounted within the casing, said casing constituting part of the electrical circuit of said elements, spaced terminals electrically connected to said ele ments and projecting through said casing and insulated therefrom, andan adjustable spark-gap'men'iber mounted upon the casing between said terminals, constituting therewith spark-gaps and adjustable to vary the distances between the terminals and the spark-gap member.

3. In an electrical condenser, a metal casing, condenser elements within the casing, the casing constituting part of the electrical circuit of said elements, terminals electrically connected to said elements and projecting through said casing at one side thereof, insulating bushings mounted on the casing and surrounding said terminals, static shields mounted upon said terminals above said bushingspreventing losses therein and comprising bell-shaped members extending laterally beyond the bushings, and a metal rod mounted upon said casing between said shields and spaced therefrom and in parallelism with the terminals, said rod having adjustably mounted thereon a conical sparkgap member forming with said shields spark-gaps, whereby upon adjustment of the member the distance between the same and both shields is varied.

4. In an electrical condenser, a casing, condenser elements Within said casing, said casing being electrically connected to certain of said elements, a high potential terminal electrically connected to said elements and projecting through said casing and insulated therefrom, said terminal being provided with a metal member projecting therefrom, and a spark-gap member elec- BEST AVAILABLE com trically connected to the casing and mounted on said casing adjacent to said metal member, and having a conical member adjustable thereon and forming with the metal member a spark-gap, whereby upon adjustment of the conical member the distance between the same and the terminal can be varied.

5. In an electrical condenser, a metal casing having a plurality of chambers therein, pairs of condenser stacks comprising alternate sheets of foil and dielectric and comprising sections connected in series and mounted horizontally within said chambers, central pressure members with which the inner ends of the stacks of each chamber engage and with which they are electrically connected, means engaging the outer ends of the stacks of each chamber and co-operating with the casing for compressing the stacks, the outer ends of the stacks being electrically connected to the casing, terminals connected to said central members and projecting through the casing, an insulating bushing surrounding each terminal whereby the terminal is insulated from the casing, a closure for an opening at one end of the easing through which a filler of insulating material may be placed, a filler of insulating material within the casing and surrounding said stacks, terminals and inner ends of the bushings, static shields mounted upon said terminals above said bushings whereby the electric field is directed in parallelism to the bushing preventing losses therein, and a spark-gap device mounted between said shields, constituting therewith spark-gaps, electrically connected to said casing and comprising an adjustable conical member cooperating with the shields, whereby upon adjustment. of the conical member the distances between the conical member and the shields are varied.

6. In a spark-gap device, metal members adapted to be at a difference of potential and spaced from each other forming a spark-gap, said members being relatively adjustable and one of the members comprising .a surface arranged at an angle to the direction of adj usting movement, whereby, upon such movement, the sparking distance between the members may be varied.

7. In a spark-gap device, a plurality of terminals and a metal casing adapted to be at a difference of potential from said terminals and insulated therefrom electrical apparatus inside said casing, different parts of said electrical apparatus being electrically connected respectively to said casing and to said terminals and a spark-gap member forming with said terminals sparkgaps and electrically connected to said casin 8. In a spark-gap device, metal members adapted to be at a difference of potential, and spaced from each other to form a spark-gap, one of said members comprising an adjustable conical member for varying the distance between the members:

9: In a spark-gap device con'iprisingtwo' metalmembers "spaced from one another and sub'ject'able' to a diiterence of p'otenti'al, and

'-s'ubjectable"to a difference" of potential, may

of sai&mem1- rs constituting a circuit'termi=- 11211 of; an electrical appara tus' and the other member being MSG-connected with such 21pparat us j an insa-lating bnsmng surrounding saimtrminn member; and-a metal shield" mounted on said t'enninai member beyond said bti's'hiiig, also spaced from" said" otlier metahmember', and pr'oteetlng the bushingalo'u fitl tli'e terminal member; Said pr'OtieCt' sliielil." and" the other member" spacedtherefrom 1 being" relatively adj ustabl'e' and constituting an adjustablespark-gap.

11* In aspark gap' device-a metal casing containing electricalapparatus aj 10w poten tial pertiea 'of whi c'h is eietrican'y connected thereto; and a pl'u'ralit'j of terminals torhi'gh' otential-pardons of said" apparatus" androjecting out thin" the casing; insulated therefrom; spactt'from'one mother outside" thecasing; and cbns'titufing" eietrodes' ot a" spar'k gapi 12. In a spark-gap device, a casing con taining eiment s' elctrieally cennected thereto, spaced: terminals 'prejeetin *th'roug-hsaid casing 'afr'id electrically conn'ected wsaid' ele mentsi, bushings insulatin saidterminals from the casinggimetar'shields mounted on the terminals" to protect the bushings 1 and constituting spark gap'i'membe'rs:

1'3. lirai sparlap' device, a metal casing, electrical elements therein electrically con-' nectedfito" the casing, a terminal connected to said elements and projecting througltthe casing; an insulating busl'n ng surrounding said terminal, a static shield mounted on the termi'i'ia'l above the bushing, a stud mounted on said casing in parallelism to said terminal 1 and electrically conne'cted to the casing" and a conical member 'adjnstable'on the stud and 1a. In a spark gap device, a'm'etal casing; electrical elements therein electrically 'connected thereto, a terminal proj ectingtl'irough the casin'g'and electrically connected to said ele1ne1its; a11' insulating bushing surrounding BEST AVAILABLE COP\ said terminal, a static shield mounted onsaid termmal above said bushing; a stud mounted on the casing and electrically connected thereto. and an adpistable member mounted on said stud and formingwith saidshield a spark ga 15. In a spark-gap device, spaced metal members adapted to'be at a difference-of potential, at least one of said members haying a curved surface, and acurved metal dvi'ce adJu'Stably mounted thereon,

curved member on which it is mounted an'd forming with the other member a spark ga said members'bemg capable of fornrmg a longer-s ark gap, upon the removal ofsaid device, the difference in length of'tlie'SparlK' gaps-being compensated for bywe'asonwf thedi'fl'erenc'e"in radii ofcurvature 'of the" curved parts to maintain the reqnrredp'ro tection;

16; In a-spark-gap device, a-meta-l -casi-ng'-,-- metal members PIOjGCtIDg'fiOH'i SErTCI casing" and insulated therefrom, spaced from'on'efairother and'subjectabletoa difierence of potential, oneof said membershavi'ng an dew trode adjustably and" r'enmrably.- mountedther'eon and forming an adjustable spark gap with the other member; and"sa'id'-nrem- I bersbeingspaced' to establish a sparkap" between themuiponthe removal of said ad justable electrode.

17. In an electrical condenser; a'me'tal cas ing', condenser elements within the casing. and'electrica'lly connected thereto'ga circuit terminal electrically connected to salid el e meirts and projecting thrti" said casing" and instflat-d therefrom; a-meta lmember mount ed on said casing; and an 'elec'ti"o'de"adjustiably" andreinev'ably mounted 'on said mem-- bet and" forming aspark gap with said 'cir cuit" terminal; saitPmetal member and-wer minal' beingspaced to est'ab1isl'1a"spark gap between themupon removal of saida'dji'istably mounted electrode.

18? In a spark' gap'dvice; spaced members having a'dja'c'ent' curved'portions, and an ad ]ust'able'curved mel'nbermounted on-one of said'first mentioned members and havingga" greater radius of curvature than'that of: the member on winch it' 15' n'rounted" and t'orming with the other membera sparlr' gap adjustable in length, said first mentioned members'being capable of formingasparkgap" upon the removal of the adjustableinen'iber.

19'. Inanelecti' ical' condenser, a"1netal casing, condenser elements'niounted within the caslng, the casing forming an 'electricalcon nection between the elements, spaced" terim nals mounted in the cas'i'ng, ins1'rlated"there fronra'nd electrically connected'to 'sa'i'd' ele= ments metal members having 'roun'ded edges and m'ounted on said terminals in' spaced apart relation, a stud secured on'said"casfn'g having" a- I i I y X t l radiusot curvature greater thanthatol' the between said'metal members, and a conical member adjustable on said stud and forming with said members adjustable spark gaps, said studhaving a smaller radius of curvature than said conical member and forming non-adjustable spark gaps with the terminal members upon the removal of the conical member, said terminal members being capable of forming a spark gap with each other upon removal of said stud.

20. In an electrical condenser, a metal casing, condenser elements therein connected in series by said casing, terminals connected to said elements, insulating material between said terminals and the casing, and static shields mounted on said terminals above the insulating material.

21. In an electrical condenser structure, the combination with the condenser itself. a metal enclosing casing therefor, and a condenser terminal projecting thru and insulated from the casing; of a metal member removably mounted on the casing and electrically connected with the condenser itself and spaced from said terminal to form a protective spark-gap therewith; and an electrode removably mounted on said removable member and also spaced from said terminal to form a protective spark-gap therewith.

22. In an electrical condenser structure. the combination with the condenser itself, a metal enclosing casing therefor and electrically connected therewith, and a condenser terminal projecting thru and insulated from the casing; of a metal member removably electrically connected with said casing and spaced from said terminal to form a protective spark-gap with the latter.

23. In an electrical condenser structure, the combination with the condenser itself, a metal enclosing casing therefor and electrically connected therewith, and a condenser terminal projecting thru and insulated from the casing and having a curved portion, of a metal member mounted on and electrically connected with the casing and having a threaded portion spaced from said curved portion of said terminal to form a protective spark-gap between the threaded portion of said metal member and the curved portion of said terminal.

24. In an electrical condenser, the combination with a stack of sheets, a metal casing therefor, and a stack-terminal projecting out thru the casing; of a spark-gap electrode electrically connected with the stack; insulating material between the stack terminal and the casing; and a metal static shield electrically connected to said terminal and operatively fixedly support-ed thereon in position relative to the casing and insulating material which protects the latter; and a spark-gap electrode adjustably spaced from said static shield to establish a protective spark-gap therewith irrespective of the BEST AVAILABLE COP\ relative positions of the static shield and casing.

25. In an electrical condenser construc tion, the combination with the condenser itself, a metal enclosing casing therefor, and a condenser terminal projecting out thru the casing; of a spark-gap electrode electrically connected to the condenser itself; insulating material between said terminal and the casing; and a metal static shield electrically connected to said terminal and mounted thereon in position relative to the casing and insulating material which protects said insulating material; said spark-gap electrode and static shield establishing between them a protective spark-gap of less length than the distance between the static shield and the casing.

26. In an electrical condenser construction, the combination with the condenser itself, a metal casing therefor, and a condenser terminal projecting out thru the casing and insulated therefrom; of an electrode sup ported on the outside of the said casing and also connected to the enclosed condenser; said electrode and terminal being spaced from one another to constitute a protective spark-gap.

27. An electrical condenser comprising a plurality of sheet-stacks; a common metal casing therefor and electrically connected therewith; a corresponding plurality of stack terminals extending out thru the casing, and metallic means electrically connected with the casing, located outside the casing, and spaced from said terminals to constitute protective spark-gaps therewith.

28. An electrical condenser comprising a plurality of sheet-stacks; a common metal casing therefor electrically connected with the ends of said stacks; a corresponding plurality of condenser terminals connected respectively to mid-points of said stacks; and metallic means supported on and electrically connected with the casing and spaced from said terminals to constitute protective sparkgaps therewith.

29. An electrical condenser comprising a plurality of sheet-stacks, a common metal casing therefor electrically connected therewith; a corresponding plurality of stack terminals extending out thru the casing and insulated therefrom; and a metal member electrically connected with and mounted on the outside of the casing, and spaced from said terminals to constitute a common spark-gap electrode establishing protective spark-gaps with said terminals; said metal member being adjustably mounted and symmetrically constructed whereby in all adjusting positions it provides equal protection for each of said plurality of stacks.

30. An electrical condenser comprising a plurality of sheet-stacks arranged end to end, a metal casing enclosing said stacks and BESTQAVAKLABLE com elctricallj connected with the outer ends 31; Inaspark-gap device; the conrbination' thereof; a condenser terminal electrically with a diskdike metal member having:- a-' 10 connected with tlfe'inner ends of said stacks curved edge, of :r cone-like metal member and extending to theontside of the casing; spaced from the'cnrvededgeand in-th'e plane 5' and' ametlrl' member electrically connected of said disk'member; said conem'em'ber'ba with and supported outsideo'f the casingan'd ingmounfiedto be adjustable"transversely of synced from said ten'nin al to establish a prothe plane of the disk'member. tective spark-gap therewith. WVILLLAM H; -PRIESS.- 

